What is primarily affected by high gross weight and low RPMs in a helicopter?

High gross weight and low RPMs in a helicopter fundamentally affect the dynamics of lift generation and blade stall characteristics, particularly in the context of retreating blade stall. When a helicopter operates at high gross weight, it demands more lift to maintain level flight. Simultaneously, if the rotor RPMs are low, the rotor blades may not be generating sufficient lift across their entire disk.

In a helicopter, the rotor blades move in a circular path, producing varying airspeeds depending on their position during rotation. The advancing blade experiences a higher relative wind speed, resulting in greater lift, whereas the retreating blade, which is moving against the relative wind, experiences reduced lift. At low RPMs combined with high weight, the vital lift required for the retreating blade to remain effective can diminish significantly, leading to a condition known as retreating blade stall. This occurs when the retreating blade's angle of attack increases beyond the critical threshold, resulting in a loss of lift and potential for a dangerous aerodynamic condition.

This phenomenon is critical for pilots to understand, as it can lead to a loss of control if not managed appropriately. In summary, under scenarios of high gross weight and low RPMs, retreating blade stall is most prominently affected, making it essential